This invention relates to the preparation of N-phosphonomethylglycine, and more particularly to an improved process for producing N-phosphonomethylglycine from an N-acylaminomethylphosphonic acid and glyoxylic acid or derivative without isolation of the N-acylaminomethylphosphonic acid or related intermediates.
N-phosphonomethylglycine is a highly effective and commercially important phytotoxicant useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. The salts of N-phosphonomethylglycine are conveniently applied in an aqueous formulation as a post emergent phytotoxicant or herbicide for the control of a broad spectrum of plant species.
Gaertner, Canadian Patent No. 1,039,739 describes a process for producing N-phosphonomethylglycine by reacting aminomethylphosphonic acid or its esters with glyoxylic acid derivatives to form carbonylaldiminomethanephosphonates. Thereafter, the carbonylaldiminomethanephosphonates are subjected to catalytic hydrogenation to produce N-phosphonomethylglycine or its esters. The ester groups can be hydrolyzed to produce N-phosphonomethylglycine.
Franz, U.S. Pat. No. 3,799,758, describes the preparation of N-phosphonomethylglycine by reacting ethyl glycinate, formaldehyde, and diethyl phosphite followed by hydrolysis. Alternative processes described by Franz include phosphinomethylation of glycine with chloromethylphosphinic acid in the presence of sodium hydroxide and oxidation of N-phosphinomethylglycine with mercuric chloride.
Moser, U.S. Pat. No. 4,369,142, describes a process for the preparation of N-phosphonomethylglycine in which aminomethylphosphonic acid is reacted in aqueous medium with glyoxal in the presence of the catalyst sulfur dioxide.
H. Yanagawa et al., "Novel Formation of .alpha.-Amino Acids and Their Derivatives from Oxo Acids and Ammonia in an Aqueous Medium", J. Biochem, 91, 2087-2090 (1982) discloses the reaction of glyoxylic acid with ammonia, methylamine, and ammonium sulfate to make glycine and/or its derivatives. On page 2088 in Table I, the synthesis of various amino acids is disclosed at pH 4 and pH 8 and at temperatures of 27.degree. C. and 105.degree. C. At the bottom of the left column bridging to the top of the right column on page 2088, it is disclosed that acidic pH and low temperatures were more favorable than alkaline pH and high temperatures for the formation of glycine.
J. Kihlberg, "Synthesis of Strombine. A New Method for Monocarboxymethylation of Primary Amines", Acta Chemica Scandinavica B 37, 911-916 (1983) discloses the reaction of two equivalents of glyoxylic acid with primary aliphatic and aromatic amines which proceeds via the initial formation of the corresponding imine derivative. In Table I, appearing on page 914, it is disclosed that various starting amines are reacted with 2 equivalents of glyoxylic acid at temperatures between about 25.degree. C. and 70.degree. C. to yield the corresponding N-formyl-N-carboxymethylamine which is easily hydrolyzed to the N-carboxymethylamine.
Kleiner, U.S. Pat. No. 4,670,191 discloses a process for the preparation of N-phosphonomethylglycine by reacting aminomethanephosphonic acid with 2 molar equivalents of glyoxylic acid at temperatures between 10.degree. C. and 100.degree. C.
Although the teachings of the above references, alone or in combination, can be used to produce satisfactory yields of N-phosphonomethylglycine, each of such teachings suffer from one or more disadvantages. Now, there is provided a straightforward process for the production of N-phosphonomethylglycine or its derivatives in good yield with inexpensive raw materials, low capital costs and simple operating procedures, without the necessity of isolating intermediate products.